Gas generator

ABSTRACT

A gas generator, including a housing made of metal and including an initiator shell and a closure shell; at least one combustion chamber formed in the housing and configured to be packed with a gas generant that generates a high temperature gas by burning; at least one filter member arranged around the at least one combustion chamber; at least one igniter located in the housing and configured to ignite and burn the gas generant in the at least one combustion chamber; and a plurality of gas discharge holes formed in the housing and configured to discharge gas generated in the at least one combustion chamber.

TECHNICAL FIELD

The present invention relates to a gas generator suitably used to expandan airbag and the like.

BACKGROUND ART

A gas generator used to expand and inflate the airbag rapidly so as toprotect a vehicle occupant from the shock at a car collision is built inan airbag module secured in a steering wheel or an instrument panel. Thegas generator operates to ignite an igniter device (squib) under controlof electrical signals from a control unit (controller) to burn enhanceragent (enhancer) and then burn gas generant by the flames of theenhancer agent, thereby generating a large amount of gas rapidly.

A so-called, double-cylinder type gas generator having a central space,equivalent to an ignition chamber of the gas generant, and an annularspace, equivalent to a combustion/filtering chamber, formed at theoutside of the central space concentrically, for burning and cooling gasand collecting slag is known as a conventional gas generator.

This type of gas generator is disclosed, for example, by JP Laid-open(Unexamined) Patent Publication No. Hei 9-207705. As shown in FIG. 8,this gas generator has a housing formed in such a manner that a centralspace of a housing structure, serving as the ignition chamber, is formedby an upper casing 51 of a double-cylinder structure and a lower casing54 of a double-short-cylinder structure being butt-welded by frictionwelding, first, and, then, an annular space, serving as thecombustion/filtering chamber, is formed around the central space. Asquib 68 and enhancer agents 69 are housed and contained in the ignitionchamber P from below. On the other hand, a ring-shaped cover member 66having a cross section of a double-flanged concave form is fixedlyplaced in the combustion/filtering chamber F, with its flanges 66 d, 66e abutted with flashes 52 b, 53 b of the upper casing 51. Gas generant57 and a cooling/slag collecting member 60 are contained in sequence inthe annular space defined between the cover member 66 and the uppercasing 51 so that they are arranged in a radial direction thereof. Thecombustion/filtering chamber F is formed in this manner. Ring-shapedcushioning members 58, 59 are provided at upper and lower sides of alayer of the gas generant 57, respectively. Also, seal members 61, 62are provided at upper and lower sides of the cooling/slag collectingmember 60, respectively. Further, an aluminum foil 64 to close a gasdischarge orifice 53 a and an aluminum foil 65 to close an enhancerorifice 52 a are adhesively bonded. With this construction, the gasgenerator that can sufficiently withstand an increased inner pressure bythe gas generated in a gas generation chamber G can be obtained.

However, this double-cylinder type gas generator requires an increasednumber of components of the gas generator and also requires acomplicated structure, as shown in FIG. 8. Due to this, there are limitsfor this type of gas generator to cut the production cost whilemaintaining the safety of the gas generator. Further, this type of gasgenerator has a small capacity to hold the gas generant. Due to this, itis mainly applied to a driver's side airbag system and is neverapplicable to a passenger's seat airbag system requiring a large amountof generated gas.

For example the gas generator shown in FIG. 9 is known as the gasgenerator for an automobile passenger's seat airbag system. As shown inFIG. 9, the conventional gas generator for the passenger's seat airbagsystem has a housing 80 comprising an outer cylinder 81 having aplurality of gas discharge holes 81 a and a cover member 82friction-welded to an end of an aperture of the outer cylinder 81. Aninner cylinder 85 is inserted and placed in the housing 80. The innercylinder 85 has gas penetrating holes 85 a, containing a prescribedamount of gas generant 86 in an interior thereof. A cylindrical burstplate 83 to close the gas discharge holes 81 a formed in the outercylinder 81 and a cylindrical filter member 84 are disposed in anannular space between the inner and outer cylinders. The cylindricalfilter member 84 is packed in the annular space as tight as possible,leaving no space therein, for the purpose of reduction in diameter ofthe housing 80. Also, an igniter device 89 comprising an igniter 87 thatignites at the detection of collision by collision sensors and enhanceragent 88 ignited by the igniter 87 is disposed in the cover member 82.

This conventional gas generator for the passenger's seat airbag systemhas a cylindrical shape, as described above, and is built in the airbagmodule secured in an interior of the instrument panel of the automobile,with its body oriented horizontally along the instrument panel and bothlengthwise ends thereof fixed therein. Due to this, a large occupiedarea is required for placement in the instrument panel. Also, the way ofand the structure for assembling the gas generator in the airbag moduleare complicated, thus involving troublesome works.

Also, owing to the cylindrical shape, it is difficult to pack the gasgenerant 86 in the interior of the housing with high packing efficiency.Obtaining an equal amount of generated gas to conventional, whilefulfilling the recent demands for reduction in size and weight of thegas generator, requires the use of gas generant that can generate moreamount of gas. Doing so requires the housing capable of wellwithstanding the high pressure at the generation of gas.

It is an object of the present invention to provide a gas generator thatcan provide a simplified structure of the gas generator and also canexhibit good gas generation performances of generating a large amount ofgas, while maintaining high safety, even when reduced in size andweight.

DISCLOSURE OF THE INVENTION

A gas generator according to the present invention comprises a housingmade of metal and having an initiator shell and a closure shell, (a)combustion chamber(s) formed in the housing and packed with gas generantthat generates high temperature gas by burning, (a) filter member(s)arranged around the combustion chamber(s), (an) igniter device(s) put inthe housing for igniting and burning the gas generant in the combustionchamber(s), and a plurality of gas discharge holes formed at the housingfor discharging gas generated in the combustion chamber(s), whereineither or both of the initiator shell and the closure shell forming thehousing has a head portion of a semispherical form or an ovalsemispherical form and a cylindrical portion of a diameter formedcontinuously from the head portion, and wherein a ratio H/D between thediameter D of the cylindrical portion and a distance H between bottomsof the head portions of the initiator shell and closure shell is in therange of 0.6-1.3. It is preferable that the diameter D is a diameter D₁between outer sides of the closure shell.

This construction can provide the result that even when the gasgenerator is reduced in number of components and is simplified instructure, deformation of the housing can be suppressed even when thepressure in the housing is increased by the gas generated by burning thegas generant in the combustion chamber. This can provide a reducednumber of components and a simplified structure, thus enabling reductionin size and weight of the gas generator and a significant reduction ofmanufacturing cost.

Also, a gas generator according to the present invention comprises ahousing made of metal and having an initiator shell and a closure shell,a combustion chamber formed in the housing and packed with gas generantthat generates high temperature gas by burning, a partition plate forpartitioning the combustion chamber into two tiered chambers, a firstfilter member and a second filter member arranged around the firstpartitioned combustion chamber and the second partitioned combustionchamber respectively, a first igniter device and a second igniter deviceput in the initiator shell for igniting and burning the gas generantpacked in the first combustion chamber and the second partitionedcombustion chamber respectively, and a plurality of gas discharge holesformed in the housing for discharging gas generated in the firstpartitioned combustion chamber and the second partitioned combustionchamber, wherein either or both of the initiator shell and the closureshell forming the housing has a head portion of a semispherical form oran oval semispherical form and a cylindrical portion of a diameter Dformed continuously from the head portion, and wherein a ratio H/Dbetween the diameter D of the cylindrical portion and a distance Hbetween bottoms of the head portions of the initiator shell and closureshell is in the range of 0.4-1.3, preferably in the form of 0.6-1.3, orfurther preferably in the range of 0.9-1.3. It is preferable that thediameter D is a diameter D₁ between outer sides of the closure shell.

This construction can provide the result that even when the housing isincreased in inner pressure using a plurality of igniter devices,deformation of the housing can be suppressed, and as such can allowreduction in size and weight. As a result of this, when the gasgenerator is used for a passenger's seat, an occupied area of the gasgenerator required for placement in the instrument panel or the like isreduced, and as such can provide an increased degree of freedom ofdesigning the instrument panel and the like.

In the gas generator of the present invention, a ratio d₁/d₂ between aminor axis d₁ and a major axis d₂ of the head portion of the initiatorshell and closure shell is in the range of 1-0.02, preferably in therange of 1-0.1, or further preferably in the range of 1-0.3.

This construction enables the housing to sufficiently withstand thepressure increase caused by the gas generated in the housing, and assuch can allow reduction in size and weight of the housing.

In the gas generator of the present invention, the head portion has across section of a generally semicircular shape or a generallysemi-elliptical shape formed with at least three continuously extendingstraight lines.

This construction can facilitate the manufacturing of the housing.

In the gas generator of the present invention, the head portion has asemi-spherical form having a curvature radius R, and a ratio D/R betweenthe diameter D of the cylindrical portion and the curvature radius R isin the range of 0.3-2, preferably in the range of 0.9-2, or furtherpreferably in the range of 1.2-2. It is preferable that the diameter Dis a length D₁ between outer sides of the closure shell. Also, R is acurvature radius of the semicircular head portion of the closure shell.

This construction enables the housing to sufficiently withstand thepressure increase caused by the gas generated in the housing. Also, thiscan facilitate the manufacturing of the housing, enabling reduction insize and weight of the housing.

In the gas generator of the present invention, the cylindrical portionformed in the closure shell has a height h of not less than 5 mm,preferable not less than 10 mm, or further preferably in the range of10-30 mm.

This construction can allow the use of a seal strip as a seal member forsealing the gas discharge holes, and as such can allow the use of theseal strip as a rupture member.

In the gas generator of the present invention, the filter member isformed so that a portion thereof around the gas discharge holes isthicker than either of an upper end portion thereof and a lower endportion thereof.

This construction can prevent the filter member from being damaged at aportion thereof on which the gas is locally concentrated whendischarged, and as such can allow the effective cooling of the gasgenerated in the housing. This can also allow the effective collectionof residuals in the generated gas.

In the gas generator of the present invention, the gas discharge holesare arranged in zigzag on a surface of the housing.

This construction can prevent concentration of the gas generated in thehousing when discharged, and as such can allow the effective use of thefilter member.

In the gas generator of the present invention, the igniter devicecomprises an inner cylinder having a base and a plurality of enhancerholes therearound, enhancer agent packed in the inner cylinder, and anigniter placed in contact with the enhancer agent.

This construction can ensure that the enhancer agent is ignited by theoperation of the igniter and then the frames from the igniter device aretransmitted to the gas generant packed in the combustion chamber.

In the gas generator of the present invention, the enhancer holes arearranged in zigzag on a surface of the inner cylinder.

This construction enables a heat current spurted from the igniter deviceto be transmitted to the entire combustion chamber, thus enabling theeffective burning of the gas generant.

In the gas generator of the present invention, the each enhancer hole isformed on a surface of cylindrical portion of the inner cylinder in theform of a slot long along an axial direction thereof.

This construction can provide adaptability to meet an axially expandedform of the combustion chamber.

In the gas generator of the present invention, the first igniter deviceand the second igniter device comprise first and second inner cylinderseach having a base and a plurality of enhancer holes therearound,enhancer agent packed in the first inner cylinder and the second innercylinder, and a first igniter and a second igniter both being placed incontact with the enhancer agent, respectively

This construction can ensure that the enhancer agents packed in bothinner cylinders are ignited by the operation of the igniter and then theframes from both igniter devices are transmitted to the gas generantspacked in the both partitioned combustion chambers.

In the gas generator of the present invention, the enhancer holes arearranged in zigzag on surfaces of the first inner cylinder and thesecond inner cylinder respectively.

This construction enables heat currents spurted from the both igniterdevices to be transmitted to the entire partitioned combustion chambers,thus enabling the effective burning of the gas generant packed in theboth combustion chambers.

In the gas generator of the present invention, the each enhancer hole isformed on surfaces of cylindrical portions of the first inner cylinderand second inner cylinder in the form of a slot long along axialdirections thereof.

This construction can provide adaptability to meet an axially expandedform of the combustion chamber.

In the gas generator of the present invention, either of the first innercylinder and the second inner cylinder has a height enough to be locatedin the second combustion chamber which is an upper side chamber of thetwo partitioned chambers.

This construction can allow the placement of the igniter devices forburning the gas generants packed in the respective combustion chamberseven when the first inner cylinder and the second inner cylinder arearranged in parallel.

In the gas generator of the present invention, the enhancer holes whichare formed at either of the first inner cylinder and the second innercylinder in the form of a cylinder having an extended axis, are formedto open only in the second combustion chamber which is located on anupper side of the two partitioned chambers.

This construction enables the gas generants packed in the respectivepartitioned combustion chambers to be burnt by their respective igniterdevices provided in the respective combustion chambers. This enables thecontrol of the generation of gas on a chamber-by-chamber basis.

In the gas generator of the present invention, the partition plate isheld in sandwich relation between the initiator shell and the closureshell.

This construction enables the combustion chamber in the housing to bepartitioned into two chambers reliably with a reduced number ofcomponents.

Also, a gas generator of the present invention comprises a housing madeof metal and having an initiator shell and a closure shell, a combustionchamber formed in the housing and packed with gas generant thatgenerates high temperature gas by burning, a filter member arrangedaround the combustion chamber, an igniter device put in the housing forigniting and burning the gas generant in the combustion chamber, and aplurality of gas discharge holes formed at the housing for discharginggas generated in the combustion chamber, wherein the housing has agenerally spherical form.

Also, a gas generator of the present invention comprises a housing madeof metal and having an initiator shell and a closure shell, a combustionchamber formed in the housing and packed with gas generant thatgenerates high temperature gas by burning, a filter member arrangedaround the combustion chamber, an igniter device put in the housing forigniting and burning the gas generant in the combustion chamber, and aplurality of gas discharge holes formed at the housing for discharginggas generated in the combustion chamber, wherein the housing has agenerally oval spherical form.

The gas generant packed in the gas generator of the present invention isin the form of a hollow body closed at both ends, or preferably in theform of a hollow cylinder closed at both ends.

This construction can produce the gas generator having the property thata weak output power is generated for a while after ignition andthereafter the output power is increased rapidly. This is because thegas generants having that form provides two ways of burning. First, onlytheir outside surfaces are burnt until their closed ends are openedafter ignited, so that the gas is generated at a gentle speed. Afterthat, their outside surfaces and inside surfaces are both burnt, so thatthe gas is generated at a drastically increased speed. The gas generantof this form draws an S-shaped curve which is considered as apreferable, pressure-in-tank-time curve for reducing the risk harming ofthe airbag.

Also, since the gas generant of this form is closed at the oppositeends, it is high in compressive strength, as compared with the one of asingle-hole cylinder form, and thus is not easily affected by vibration.Accordingly, the gas generator having the stable combustion propertiescan be obtained even after it is mounted on the automobile for a longperiod. Further, since the gas generant in the form of a hollow bodyclosed at both ends has a high compressive strength, the gas generantscan be packed in the combustion chamber with high density, thusproducing the gas generator which is further reduced in size and weight.

In a passenger's seat airbag module of the present invention, the gasgenerator of the present invention is fixed to a gas generator holdingportion of the airbag module by a flanged portion of the gas generatorin such a condition that the gas discharge holes are located in theairbag.

This construction enables reduction in size of the airbag module, ascompared with the conventional passenger's seat gas generator. That isto say, the conventional passenger's seat gas generator has acylindrical shape and is fixed to the gas generator holding portion ofthe airbag module at both lengthwise ends thereof, with its cylindricalportion oriented horizontally. Since the gas discharged holes are in thecylindrical portion, the gas generator holding portion is so structuredas to cover the entire gas generator. Also, since the passenger's seatgas generator is set in the instrument panel located in a place distantfrom a vehicle occupant, increase in amount of gas generated isrequired, and the cylindrical portion is also elongated. This inevitablyleads to increase in size of the airbag module in which the conventionalpassenger's seat gas generator is assembled. In contrast to this, in thegas generator of the present invention, since the cylindrical portionhaving the gas discharge holes is oriented vertically and also is fixedto the gas generator holding portion of the airbag module via theflanged portion located at the cylindrical portion, there is no need forthe gas generator holding portion to cover the entire gas generator.Also, the gas generator of the present invention is smaller in size thanthe conventional passenger's seat gas generator, and as such can allowreduction in size of the airbag module.

In addition, since there is no need to cover the entire gas generator,as the airbag module using the conventional passenger's seat gasgenerator does, the structure of the gas generator holding portion ofthe airbag module can also be simplified.

The airbag module of the present invention has a single gas generator.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of a gas generator of an example of anembodiment of the present invention.

FIG. 2 an external view of the gas generator of the embodiment of thepresent invention.

FIG. 3 is a sectional view of the gas generator of another embodiment ofthe present invention.

FIG. 4 is a sectional view of the gas generator of another embodiment ofthe present invention.

FIG. 5 is a sectional view of the gas generator of another embodiment ofthe present invention.

FIG. 6 is a sectional view of the gas generator of another embodiment ofthe present invention.

FIG. 7 is an illustration for explaining a relation between a minor axisd₁ and a major axis d₂ of a head portion of the gas generator accordingto the embodiment of the present invention.

FIG. 8 is a sectional view showing an example of a conventional doublecylinder type gas generator.

FIG. 9 is a sectional view showing an example of a conventionalpassenger's seat gas generator.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, certain preferred embodiments of a gas generatoraccording to the present invention will be described with reference toaccompanying drawings.

Referring to FIG. 1, there is shown a sectional view of a gas generatorA1 according to an example of an embodiment of the present invention.The gas generator A1 is used to expand and inflate an airbag. Itcomprises a housing 3 of a generally spherical form having an initiatorshell 1 and a closure shell 2 which are made of metal, such as iron,stainless, aluminum, and steel, a combustion chamber 5 formed in thehousing 3 and packed with gas generants 4 that generate high temperaturegas by burning, a filter member 6 arranged around the combustion chamber5, and an igniter device 7 secured in the housing 3 for igniting andburning the gas generants 4 in the combustion chamber 5.

The closure shell 2 comprises a cylindrical portion 9 having a diameterD, a head portion 10 of a semispherical form formed continuously fromthe cylindrical portion 9, and a flange portion 12 extending radiallyoutwardly from the cylindrical portion 9. A plurality of gas dischargeholes 8 are arranged preferably in zigzag on a surface of thecylindrical portion 9 (See FIG. 2). The gas discharge holes 8 arrangedin zigzag allow the gas generated in the housing 3 to be discharged in adispersed state without concentration. This prevents the filter member 6from being damaged. Also, this can allow the filter member 6 to be usedin a wide range, providing efficient use of the filter member 6. Thesegas discharge holes 8 may be formed to be arranged in rows, such as e.g.in two rows or three rows, as well as in zigzag. The same effect can beproduced by such an alternative arrangement.

Also, the gas discharge holes 8 may be arranged so that large diameterones and small diameter ones can be arranged alternately, without beinglimited only to the ones having a uniform diameter. They may be arrangedin several rows, such as three rows, four rows, etc., without beinglimited to the two-row arrangement along an axis direction of thecylindrical portion 9 as shown in FIG. 2. Also, they may be formed tohave several different diameters, such as for example three or fourdifferent diameters, without being limited to two different diameters.Thus, controlling the diameter of the gas discharge holes 8 can producea controlled inner pressure of the housing 3. For example, increasingthe diameter of the gas discharge holes 8 can suppress a pressure risein the housing 3. This can also allow reduction in wall thickness of theclosure shell 2 and initiator shell 1 of the housing 3 in accordancewith an inner pressure of the housing 3. Also, controlling the diameterof the gas discharge holes in accordance with the kind of the gasgenerant 4 used can produce controlled gas generation properties. Thewall thickness of the initiator shell 1 and the closure shell 2 ispreferably in the range of 1.5 mm to 3 mm.

A rupture member 11, such as a strip aluminum tape, is adhesively bondedto around the inside of the cylindrical portion 9 to close the gasdischarge holes 8 so as to seal the interior of the combustion chamber 5tightly. A height h of the cylindrical portion 9 is usually 5 mm ormore, preferably in the range of 5-30 mm, or further preferably in therange of 10-30 mm. This is because this can allow the use of the rupturemember 11 in the form of a strip tape and can also allow the adhesivebonding of the rupture member 11 with ease and reliability.

A ratio d₁/d₂ between a minor axis d₁ and a major axis d₂ of the headportion 10 is in the range of 1-0.02, preferably in the range of 1-0.1,or further preferably in the range of 1-0.3. When the minor axis-majoraxis ratio is in this range, the housing can sufficiently withstand theinner pressure resulting from the gas generated in the gas generator.

The head portion 10 has the minor axis d₁ and the major axis d₂ as shownin FIG. 7. Where the ratio d₁/d₂ is 1, the head portion 10 has asemispherical shape.

When the head portion 10 has a semispherical shape, it is preferablethat a ratio D/R between a curvature radius R of the head portion 10 anda diameter D of the cylindrical portion 9 is usually in the range of0.3-2, preferably in the range of 0.9-2, or further preferably in therange of 1.2-2. It is preferable that the diameter D of the cylindricalportion 9 has a value of a length D₁ shown in FIG. 1 as mentioned later.The curvature radius R is a curvature radius of a top portion of thehead portion 10.

Forming the head portion in a semispherical shape or an ovalsemispherical shape can prevent local concentration of gas pressuregenerated in the combustion chamber 5 on any area of the head portion.Consequently, even when the gas generator is reduced in number ofcomponents and is simplified in structure, deformation of the housing atthe time of the generation of gas can be suppressed to a very smallrange.

The initiator shell 1 joined to the closure shell 2 by pressure weldingor welding comprises a cylindrical portion 13 and a head portion 14 of asemispherical form formed continuously from the cylindrical portion 13,as is the case with the closure shell 2 mentioned above. An igniterdevice 7 is provided in a center of the head portion 14. The provisionof the cylindrical portion 13 can facilitate the joining of theinitiator shell to the closure shell 2 by pressure welding, welding orthe like. The cylindrical portion 13 is not indispensable, in otherwords, the initiator shell 1 can be formed by the head portion 14 only,as long as the initiator shell can be joined directly to the closureshell 2 at the ends of the head portion 14 by pressure welding, weldingor the like.

The head portion 14 of the initiator shell 1 has a ratio d₁/d₂ between aminor axis d₁ and a major axis d₂ of the head portion 14 is in the rangeof 1-0.02, preferably in the range of 1-0.1, or further preferably inthe range of 1-0.3, as is the case with the head portion 10 of theclosure shell 2 mentioned above. This can provide the result that whenthe initiator shell 1 and the closure shell 2 are joined together, thehousing 3 of a generally spherical shape or a generally ovalsemispherical shape can be formed.

The igniter device 7 provided in the center of the head portion 14comprises an inner cylinder 16 having a based and a plurality ofenhancer holes 15 around it, enhancer agent 17 packed in the innercylinder 16, and an igniter 18 disposed in contact with the enhanceragent 17. The enhancer agent is used for ensuring the initiation of theburning of the gas generant. Composition comprising metal powder and anoxidizing agent typified by B/KNO₃ which is in common use, compositioncomprising a nitrogen-contained compound, an oxidizing agent and metalpowder, or composition of gas generant may be used as the enhancer agent17. The enhancer agent 17 contains the respective components in variousratios mentioned below. The enhancer agent 17 comprising metal powderand oxidizing agent preferably contains a 1-30 weight % metal powdercomponent and a 70-95 weight % oxidizing agent component. The enhanceragent 17 comprising a nitrogen-contained compound, an oxidizing agentand metal powder preferably contains a 1-30 weight % metal powdercomponent, a 0-40 weight % nitrogen-contained organic compound, and a50-90 weight % oxidizing agent component. It may contain a 0-10 weight %molding binder, if necessary. The molding binder that may be generallyused for the gas generant can be used. The enhancer agent 17 of powderyform, granular form, columnar form, sheet-like form, spherical form,single-pore cylinder form, multiple-pore cylinder form, tablet form, orin the form of a molded cylinder closed at both ends may be used.

The inner cylinder 16 is fixed to an igniter device holding portion 19by a proper method, e.g., by crimping, and in turn to the initiatorshell 1 by fixing the igniter device holding portion 19 to the headportion 14 by a proper method, e.g., by welding. The inner cylinder 16is in the form of an elongate cylinder extending form one end of thecombustion chamber 5 formed in the housing 3 to a nearly center of thecombustion chamber 5. A plurality of enhancer holes 15 in the form of acircular hole or a slotted hole are formed around the inner cylinder 16and are arranged usually in zigzag along an axial direction of the innercylinder 16. It is preferable that the enhancer holes 15 are arranged inzigzag, as shown in FIG. 1, so that neighboring holes are not arrangedin line with each other along the axial direction of the inner cylinder16. This can allow the efficient spurting of the heat current spurtedfrom the igniter device 7 into the entire combustion chamber 5.

A filter member 6 is provided in the housing 3 formed by the closureshell 2 and the initiator shell 1, extending along inner walls of thecylindrical portions 9, 13. The filter member 6 is produced at a lowcost by forming e.g. a knitted wire sheet, a plain-woven wire sheet, oran aggregation of crimped metal wire rods or stamped metal wire rodsinto a circular shape. The filter member 6 is held on the inside wall ofthe housing 3 via holders 20, 21 provided on inner surfaces of the headportions 10, 14 of the closure shell 2 and the initiator shell 1,respectively.

A filter holding member 24 is arranged around the outside of the filtermember 6 at a periphery thereof adjacent to the gas discharge holes 8.The filter holding member 24 is a plate-like member with a plurality ofholes, which is called a punching metal, formed into a ring-like shape.This filter holding member 24 arranged around the outside of the filtermember 6 at the periphery thereof adjacent to the gas discharge holes 8restrains the filter member 6 from being deformed by the pressure of gasdischarged.

The gas generants 4 are packed in a space around the inside of thefilter member 6, and the space serves as the combustion chamber 5 wherethe gas generants 4 are burnt by the heat current from the igniterdevice 7.

The gas generants 4 that may be used include non-azide compositioncomprising e.g. fuel, an oxidizing agent, and additives (a binder, aslag forming agent, a combustion regulator).

The fuels that may be used include, for example, a nitrogen-containedcompound. The nitrogen-contained compounds that may be used include, forexample, a mixture of one or at least two materials selected from thegroup containing of triazole derivative, tetrazole derivative, guanidinederivative, azodicarbonamide derivative, hydrazine derivative, ureaderivative, and ammine complex.

Concrete examples of the triazole derivative include, for example,5-oxo-1,2,4-triazole and aminotriazole. Concrete examples of thetetrazole derivative include, for example, tetrazole, 5-aminotetrazole,aminotetrazole nitrate, nitroaminotetrazole, 5,5′-bi-1H-tetrazole,5,5′-bi-1H-tetrazole diammonium salt, and 5,5′-azotetrazole diguanidiumsalt. Concrete examples of the guanidine derivative include, forexample, guanidine, nitroguanidine, cyanoguanidine, triaminoguanidinenitrate salt, guanidine nitrate, aminoguanidine nitrate, and guanidinecarbonate. Concrete examples of the azodicarbonamide derivative include,for example, azodicarbonamide. Concrete examples of the hydrazinederivative include, for example, carbohydrazide, carbohydrazide nitratesalt complex, dihydrazide oxalate, and hydrazine nitrate salt complex.Concrete examples of the urea derivative include, for example, biuret.Concrete examples of the ammine complex include, for example, hexamminecopper complex, hexammine cobalt complex, tetrammine copper complex, andtetrammine zinc complex.

Of these nitrogen-contained compounds, one or at least two materialsselected from the group consisting of tetrazole derivative and guanidinederivative is preferable. Particularly preferable are nitroguanidine,guanidine nitrate, cyanoguanidine, 5-aminoterazole, aminoguanidinenitrate and guanidine carbonate.

It is preferable that a mixing proportion of these nitrogen-containedcompounds in the gas generant 4 is usually in the range of 20-70 weight%, or particularly preferably in the range of 30-60 weight %, dependingon the number of carbon atoms, hydrogen atoms, and other atoms oxidizedin the molecular formula. An absolute numerical value of the mixingproportion of the nitrogen-contained compounds varies depending on thekinds of oxidizing agent added to the gas generant. However, when anabsolute numerical value of the mixing proportion of nitrogen-containedcompounds is larger than the theoretical total oxidation amount,concentration of trace CO in the generated gas increases. On the otherhand, when the absolute numerical value of the mixing proportion ofnitrogen-contained compounds is equal to or less than the theoreticaltotal oxidation amount, concentration of trace NOx in the generated gasincreases. Accordingly, it is most preferable that the mixing proportionof nitrogen-contained compounds is in the range in which an optimumbalance of the both can be made.

The oxidizing agent selected from at least one material of nitrate,nitrite and perchlorate, each including cation, selected from alkalinemetal, alkaline earth metal, transition metal and ammonium ispreferable. Although the oxidizing agents other than nitrate, i.e.,nitrite and perchlorate, both of which are in heavy use as the oxidizingagent in the field of airbag inflator, can also be used, nitrate ispreferably used from the viewpoints that the oxygen number in themolecules of nitrite is reduced, as compared with that of nitrate andthat generation of finely-powdered mist that is easily released out fromthe airbag is reduced. Examples of the nitrate include, for example,sodium nitrate, potassium nitrate, magnesium nitrate, strontium nitrate,phase stabilized ammonium nitrate, and basic copper nitrate. Strontiumnitrate, phase stabilized ammonium nitrate, and basic copper nitrate arepreferably used.

It is preferable that a mixing proportion of the oxidizing agent in thegas generant is preferably in the range of 30-80 weight %, orparticularly preferably in the range of 40-75 weight % with respect tothe CO concentration and NOx concentration described above, depending ona kind and a quantity of nitrogen-contained compound used.

Any binder of the additives may be used as long as it does not exert asignificant negative effect on the burning behavior of the gas generant.Examples of the binder include, for example, metal salt such ascarboxymethyl cellulose; polysaccharide derivative such as methylcellulose, hydroxylmethyl cellulose, cellulose acetate, cellulosepropionate, cellulose acetate butyrate, nitrocellulose, microcrystallinecellulose, guar gum, polyvinyl alcohol, polyacrylamide, and starch;organic binder such as stearic acid salt; and inorganic binder such asmolybdenum disulfide, synthetic hydroxytalcite, acid clay, talc,bentonite, diatomite, kaolin, silica, and alumina.

It is preferable that a mixing proportion of the binder is in the rangeof 0-10 weight % for a press molding, or in the range of 2-15 weight %for an extrusion molding. As a quantity of binder added increases,breaking strength of a molded product increases, but, the carbon atomnumber and hydrogen atom number in the composition increases alongtherewith, resulting in that concentration of trace CO gas which is anincomplete combustion product increases and quality of generated gasdeteriorates. That also hinders the combustion of the gas generant. Inview of this, a minimum amount of binder should preferably be used.Particularly a proportion of the binder in excess of 15 weight %requires increase of a relative abundance ratio of the oxidizing agent,causing reduction of a relative ratio of the gas generation compound andthus making it difficult to establish a practicable gas generationsystem.

Also, the slag forming agent may be mixed as the other components ofadditives than the binder. The slag forming agent is added, for thepurpose of facilitating the filtration of the filter in the gasgenerator through the interaction with metal oxide produced fromcomponents of the gas generant, particularly from components of theoxidizing agent.

Examples of the slag forming agent include, for example, those selectedfrom silicon nitride, silicon carbide, acid clay, silica, naturallyoccurring clay containing bentonite-based or kaolin-basedaluminosilicate as a major component, artificial clay, such as syntheticmica, synthetic kaolinite and synthetic smectite, and talc which is oneof hydrous magnesium silicate minerals. Of these slag forming agents,acid clay or silica, particularly acid clay, is preferably used. Amixing proportion of the slag forming agent is preferably in the rangeof 0-20 weight %, or particularly preferably in the range of 2-10 weight%. When an excessive amount of lag forming agent is added, a linearcombustion velocity and gas generation efficiency are reduced, while onthe other hand, when an even smaller amount of slag forming agent isadded, the slag forming performances cannot be provided sufficiently.

Gas generant comprising 5-aminotetrazole, strontium nitrate, synthetichydrotalcite and silicon nitride, or gas generant comprising guanidinenitrate, strontium nitrate, basic copper nitrate and acid clay can becited as an example of a preferable combination of components of the gasgenerant.

Also, the combustion regulator may be added, if necessary. The fuelregulators that may be used include, for example, metal oxide,ferrosilicon, activated charcoal, graphite, and a chemically combinedexplosive, such as hexogen, octogen and 5-oxo-3-nitro-1,2,4-triazole. Amixing proportion of the combustion regulator is preferably in the rangeof 0-20 weight %, or particularly preferably in the range of 2-10 weight%. When an excessive amount of combustion regulator is added, the gasgeneration efficiency is reduced, while on the other hand, when an evensmaller amount of combustion regulator is added, a sufficient combustionvelocity cannot be obtained.

The gas generant of pellet form, columnar form, single-pore cylinderform, multiple-pore cylinder form, disk form, or in the form of a hollowcylinder closed at both ends may be used. Preferably, the gas generantin the form of a hollow cylinder closed at both ends may be used.

An example of the method of producing the gas generant in the form of ahollow cylinder closed at both ends is described. First, non-azidecomposition comprising the nitrogen-contained compound, oxidizing agent,slag forming agent, and binder is mixed by a V type mixer, a ball milland the like. Then, water or solvent (e.g. ethanol) is added and mixedwith the mixture being stirred, to thereby produce a clod of powderedmixture in a moist state. It should be noted here that the term “themoist state” means a state in which the clod of powdered mixture hassome degree of plasticity, containing water or solvent in the range of10-25%, or preferably in the range of 13-18 weight %. Thereafter, theclod of powdered mixture in the moisture state is extruded through anextruder (e.g. the one having a die and an inner-hole pin at its outletport) as it is, to mold the clod into a hollow cylinder form having anouter diameter preferably in the range of 1.4 mm-4 mm, or furtherpreferably in the range of 1.5 mm-3.5 mm, and an inner diameterpreferably in the range of 0.3 mm-1.2 mm, or further preferably in therange of 0.5 mm-1.2 mm. Thereafter, the molded products in the form of ahollow cylinder are thrust at a uniform interval to produce the moldedproducts in the form of the cylinder closed at both ends. Usually, afterthe molded products in the form of the hollow cylinder are thrust in auniform interval, they are cut off in such a manner that they are foldedat their closed dent portions. Thereafter, they are dried in two stages:they are dried at temperature usually in the range of 50-60° C. for 4-10hours, first, and, then, dried at temperature usually in the range of105-120° C. for 6-10 hours. The gas generants in the form of thecylinder closed at both ends thereof and having a space therein areproduced in the manner described above. The gas generants thus producedhave a length usually in the range of 1.5-8 mm, preferably in the rangeof 1.5-7 mm, or further preferably in the range of 2-6.5 mm.

The linear combustion velocity of the gas generants is measured in aconstant pressure condition and is experientially determined inaccordance with the formula of Vielle given below.r=aP^(n)where r represents a linear combustion velocity, a represents aconstant, P represents a pressure, and n represents a pressure exponent.The pressure exponent n indicates a slope from a logarithmic plot inwhich the pressure taken as the X-axis is plotted against the log ofcombustion velocity taken as the Y-axis.

Preferably, the linear combustion velocity of the gas generant used forthe gas generator of this embodiment is in the range of 3-60 mm/sec. orpreferably in the range of 5-35 mm/sec. under the pressure of 70 kgf/cm²and the pressure exponent is in the range of n=0.90 or less, preferablyin the range of n=0.75 or less, or particularly preferably in the rangeof n=0.60 or less.

The linear combustion velocity can be measured by the generalmeasurement method including the strand burner method, the small motormethod, and the sealed pressure container method. To be more specific,the combustion velocity is measured in a high-pressure container by thefuse cut-out method and the like using a test piece obtained by beingpress-molded in a prescribed size, followed by being coated with arestrictor. In this measurement, with the pressure in the high-pressurecontainer as a parameter, the linear combustion velocity is measured andthen the pressure exponent is determined from the formula of Vielleabove.

Cushioning members 22 are provided in the combustion chamber 5 on a sidethereof on which the head portion 10 of the closure shell 2 is. Thesecushioning members 22 are formed, for example, of ceramics fibers,silicon foam and the like, to prevent damage, such as crack, of the gasgenerants 4 packed in the combustion chamber 5 caused by vibration andthe like.

The housing 3 formed by joining together the initiator shell 1 and theclosure shell 2 has a ratio H/D between a distance H between bottoms ofthe head portions 14, 10 of the initiator shell 1 and the closure shell2 and the diameter D of the cylindrical portion 9 which is set to beusually in the range of 0.4-1.3, preferably in the range of 0.6-1.3, orfurther preferably in the range of 0.9-1.3. The setting of the H/D ratioin this range enables reduction in size and weight of the gas generator,while providing to the gas generator sufficient strength to withstandthe pressure resulting from the gas generated in the combustion chamber5.

In addition, the setting of the ratio H/D of the cylindrical portion 9,13 to the diameter D to be in the range of 0.4-1.3, preferably in therange of 0.6-1.3, or further preferably in the range of 0.9-1.3 canallow the gas generants 4 to be packed with ease as well as with highefficiency, even when the gas generator is reduced in size and weight.Incidentally, for example when the gas generator according to thisembodiment is used with the automobile passenger's seat airbag, the H ispreferably set to be in the range of not less than 45 mm to not morethan 90 mm. Thus, even when the gas generator is reduced in size andweight, it can be packed with an equal quantity of gas generant toconventional, and as such can prevent reduction in amount of generatedgas. Again, the gas generator can be reduced in size and weight whilegenerating an equal quantity of gas to conventional. This is becausesince the housing includes the head portion 14, 10 formed as describedabove, the housing does not have any interior area which is subjected toa local pressure concentration and therefore can well withstand the highpressure, suppressing deformation of the housing at the time ofgeneration of gas to a very small range.

The gas generator A1 thus constructed in the form of a single-cylindergas generator is assembled mainly in the airbag module secured in theinstrument panel on the passenger seat side.

The assembling of the gas generator in the airbag module can be effectedby fixing the flange 12 to the module. Thus, the gas generator of theinvention does not require any complicated work in assembling in themodule, as the conventional cylindrical gas generator used for thepassenger's seat airbag does, enabling a very easy assembling of the gasgenerator in the module. Also, as a result of the gas generator beingreduced in size and weight, an occupied area of the gas generatorrequired for placement in the instrument panel is reduced. This canprovide an increased degree of freedom of designing the instrumentpanel.

Then, after the gas generator A1 is assembled in the airbag module, theigniter device 7 of the gas generator A1 is connected to a connector onthe vehicle side, not shown. The gas generator A1 can be used with theairbag on the driver's side as well.

In the gas generator A1 connected to the automobile in the manner asdescribed above, for example when automobile collision is detected bythe collision sensor, the igniter device 7 is operated through a squibignition circuit connected to the igniter device 7, to burn the gasgenerants 4 in the combustion chamber 5 to thereby generate hightemperature gas. Although the pressure in the interior of the combustionchamber 5 increases at that time, since the housing 3 has asemispherical form, the housing 3 has a sufficient strength to withstandthe pressure increase in the combustion chamber 5, suppressingdeformation of the housing to a very small range. Then, the hightemperature gas generated in the combustion chamber 5 passes through thefilter member 6, bursts the rupture member 11, and is discharged fromthe gas discharge holes 8. When the high temperature gas passes throughthe filter member 6, the gas is cooled down and its residual iscollected through the filter member 6. Also, since the filter member 6is arranged to cover nearly the entire area of the combustion chamber 5,an effective use of the filter member 6 can be made. This enables theeffective cooling of the gas and the effective collection of theresidual of the gas before discharged.

The gas generator according to the present invention is not limited tothe above-illustrated example of the first embodiment. For example, asshown in FIG. 3, the filter member 6 placed in the combustion chamber 5may be modified to have a larger wall thickness at a portion thereofaround the gas discharge holes 8 than at either of an upper end portionthereof and a lower end portion thereof. Also, the filter member 6 maybe tapered to gradually become reduced in wall thickness from its upperend to its lower end, though not shown.

This modification of the filter member 6 to have a larger wall thicknessat a portion thereof around the gas discharge holes 8 than at either ofan upper end portion thereof and a lower end portion thereof can producethe result that even when the gas generated in the combustion chamber 5is locally concentrated on a portion of the filter member around the gasdischarge holes 8 when discharged, the damage to the filter member 6 canbe restrained. This can prevent damage to the functions of the filtermember 6 of cooling the gas and collecting the residual.

Also, either or both of the head portions 10, 14 of the closure shell 2and the initiation shell 1 may be formed to have a cross section of agenerally semicircular form or a generally semi-elliptical form formedby three or more continuously extending straight lines, as shown in FIG.4. This configuration can suppress the stress concentration even whenthe pressure in the housing increases, and as such can also allowreduction in size and weight of the housing. This can also facilitatethe manufacturing of the housing.

Alternatively, one of the head portion 14 of the initiator shell 1 andthe head portion 10 of the closure shell 2 may be formed to have a crosssection of a semicircular form and the other may be formed to have across section of a semi-elliptical form, though not shown.

Additionally, the gas generator according to the present invention maybe constructed so that the interior of the housing 3 is partitioned intotwo tiered spaces by e.g. a partition plate 30, as shown in FIG. 5,without being limited to the example and variants of the embodimentillustrated above. The same reference numerals/characters in FIG. 5 asthose in FIGS. 1-4 refer to corresponding parts, and detaileddescription thereon is omitted.

The gas generator A2 shown in FIG. 5 comprises a metal housing 3 formedby an initiator shell 1 and a closure shell 2, a combustion chamber 5formed in the housing 3 and packed with gas generants 4 that generatehigh temperature gas by burning, and a partition plate 30 forpartitioning the combustion chamber 5 into two tiered chambers. It alsocomprises first and second filter members 6 a and 6 b arranged aroundthe inside of the first and second combustion chambers 5 a and 5 bpartitioned by the partition plate 30, first and second igniter devices7 a, 7 b secured to the initiator shell 1 for igniting and burning thegas generants 4 packed in the first and second combustion chambers 5 a,5 b partitioned by the partition plate 30, and a plurality of gasdischarge holes 8 formed in the housing 3 for discharging the gasgenerated in the first and second partitioned combustion chambers 5 a, 5b therefrom.

Either or both of the initiation shell 1 and the closure shell 2 formingthe housing 3 have semicircular or semi-elliptical head portions 14, 10,and cylindrical portions 13, 9 having a diameter D formed continuouslyfrom the head portions 14, 10. The ratio H/D between the distance Hbetween bottoms of the head portions 14, 10 of the initiator shell 1 andclosure shell 2 and the diameter D of the cylindrical portion 9 isusually in the range of 0.4-1.3, preferably in the range of 0.6-1.3, orfurther preferably in the range of 0.9-1.3. The diameter D of thecylindrical portion 9 is preferably taken as a length D₁ shown in FIG.5, as mentioned later.

The partition plate 30 for partitioning the combustion chamber 5 in thehousing 3 into the two tiered chambers of the first and secondcombustion chamber 5 a, 5 b has a partition portion 31 and a flangedportion 32 formed by pressing a sheet of plate material, as shown inFIG. 5. The partition portion 31 has a hole 33 for insertion of a secondinner cylinder 16 b of a second igniter device 7 b mentioned later. Astepped portion 34 is formed around the hole 33. The second cylinder 16b is restrained with its stepped portion 16 c held by the steppedportion 34. The partition plate 30 is fixed with its flanged portion 32held in sandwich relation between joining portions of the initiatorshell 1 and the closure shell 2.

The first igniter device 7 a and the second igniter device 7 b forburning the gas genetants 4 packed in the combustion chambers 5 a, 5 bare provided in the two-tiered, first and second combustion chambers 5a, 5 b defined by the partition plate 30, respectively.

The first igniter device 7 a provided in the first combustion chamber 5a formed on the lower side of the housing 3 comprises a first cylinder16 a having a base and a plurality of enhancer holes 15 formedtherearound, enhancer agent 17 packed in the first inner cylinder 16 a,and a first igniter device 18 a placed in contact with the enhanceragent 17.

The first inner cylinder 16 a is in the form of a closed-end cylinderhaving the same diameter and is fixed to an igniter device holdingportion 19 a by a proper method, e.g., by crimping. The first innercylinder 16 a is fixed to the initiator shell 1 by fixing the igniterdevice holding portion 19 a to the head portion 14 by a proper method,e.g., by welding. Also, the first inner cylinder 16 a has a cylindricalform extending from one end portion of the first combustion chamber 5 aformed at a lower side of the interior of the housing 3 to nearly acenter portion of the first combustion chamber 5 a. A plurality ofenhancer holes 15 in the form of a slotted hole or a circular hole areformed around the first inner cylinder 16 a and are arranged usually inzigzag along an axial direction of the first inner cylinder 16 a. It ispreferable that the enhancer holes 15 are arranged in zigzag so thatneighboring holes are not arranged in line with each other along theaxial direction of the first inner cylinder 16 a. This can allow theefficient spurting of the heat current spurted from the first igniterdevice 7 a into the entire first combustion chamber 5 a.

The second igniter device 7 b provided in the second combustion chamber5 b formed on the upper side of the housing 3 for burning the gasgenerant 4 in the second combustion chamber 5 b comprises a secondcylinder 16 b having a base and a plurality of enhancer holes 15 formedtherearound, enhancer agent 17 packed in the second inner cylinder 16 b,and a second igniter device 18 b placed in contact with the enhanceragent 17.

The second inner cylinder 16 b is in the form of a closed-end cylinderhaving a small diameter portion and a large diameter portion differentin diameter from each other and a stepped portion 16 c and is fixed tothe igniter device holding portion 19 a by a proper method, e.g., bycrimping. The second inner cylinder 16 b is fixed to the initiator shell1 by fixing the igniter device holding portion 19 a to the head portion14 by a proper method, e.g., by welding. Also, the second inner cylinder16 b has a cylindrical form extending from one end portion of the firstcombustion chamber 5 a at a lower side of the interior of the housing 3formed by the partition plate 30 to nearly a center portion of thesecond combustion chamber 5 b. A plurality of enhancer holes 15 in theform of a slotted hole or a circular hole are formed around the innercylinder on the second combustion chamber 5 b side and are arrangedusually in zigzag along an axial direction of the inner cylinder. It ispreferable that the enhancer holes 15 are arranged in zigzag on asurface of the second inner cylinder 16 b so that neighboring holes arenot arranged in line with each other along the axial direction. This canallow the efficient spurting of the heat current spurted from the secondigniter device 7 b into the entire combustion chamber 5.

Also, the second inner cylinder 16 b is fixed to the partition plate 30by crimping, screwing, and the like. In this embodiment, the secondinner cylinder 16 b is screw-threaded around the outside surface of thesmall diameter portion and is threadedly engaged with a nut 35, so thatthe second inner cylinder 16 b is fixed to the partition wall 30 withthe stepped portion 34 formed in the partition wall 30 held in sandwichrelation between the nut 35 and the stepped portion 16 c. This canensure that fixing to keep the second inner cylinder in the restrainedstate even at the operation of the second igniter 18 b. In addition,this can also ensure the fixing of the partition plate 30 to restraindeformation of the partition plate 30 caused by the pressure increase atthe time of generation of gas in the first combustion chamber 5 a. Thiscan prevent the gas from being bypassed from the first combustionchamber 5 a to the second combustion chamber 5 b.

The igniter device holding portion 19 a is formed to have a larger wallthickness at a portion thereof where the second igniter device 7 b forburning the gas generants 4 packed in the second combustion chamber 5 bis fixed than at a portion thereof where the first igniter device 7 a isfixed. This can bring the carrying and fixing position of the secondigniter 18 b near the second combustion chamber 5 b, to increase thecombustion efficiency of the gas generants 4 of the second combustionchamber 5 b. Also, a closing plug 18 c of the second igniter 18 bcarried and fixed in the large thickness portion of the igniter deviceholding portion 19 a is formed to have a long shaft length, tocorrespond in length of electrode pins 23 projecting from the closingplug 18 c to that of the first igniter 18 a. This can provide increasedstrength of the second igniter 18 b. This can also eliminate the need tochange a shape of a connector of a collision sensor and the like, notshown, connected to the electrode pins 23.

A first filter member 6 a and a second filter member 6 b are provided inthe first combustion chamber 5 a and the second combustion chamber 5 bdefined by the partition plate 30, extending along inner walls of thecylindrical portions 13, 9. These filter members 6 a, 6 b are producedat a low cost by forming e.g. a knitted wire sheet, a plain-woven wiresheet, or an aggregation of crimped metal wire rods or stamped metalwire rods into a circular shape, as is the case with the filter memberpreviously mentioned.

The gas generator A2 thus constructed, serving as a double-cylinder gasgenerator, is assembled mainly in the airbag module secured in theinstrument panel on the passenger's seat side. The first igniter device7 a and the second igniter device 7 b of the gas generator A2 areconnected to connectors on the vehicle side, not shown, respectively.This gas generator is also applicable to the airbag on the driver's seatside in that it can be reduced in size and weight.

For example when automobile collision is detected by the collisionsensor, the gas generator A2 thus connected to the automotive vehicleput the first igniter device 7 a into operation via a squib ignitioncircuit connected to the first igniter device 7 a on the firstcombustion chamber 5 a side packed with a smaller amount of gas generant4, first. This causes the gas generant 4 packed in the first combustionchamber 5 a to be burnt, thereby generating high temperature gas. Thehigh temperature gas generated in the first combustion chamber 5 apasses through the first filter member 6 a, first. Then, after it istemporarily stored in a space S1 formed between the first filter member6 a and the cylindrical portion 13, it passes through a gas passage 36formed in the flanged portion 32 of the partition plate 30 and isdischarged from the gas discharge holes 8 arranged on s surface of thecylindrical portion 9. The gas passage 36 is formed by a cutout formedat an end of the flanged portion 32, though it may be formed by athrough hole extending through the flanged portion 32.

Then, the second igniter device 7 b is put into operation in a certaintime difference. This causes the gas generants 4 in the secondcombustion chamber 5 b to be burnt, generating the high temperature gas.The high temperature gas generated in the second combustion chamber 5 bpasses through the second filter member 6 b, first. Then, after it ismixed with the high temperature gas from the first combustion chamber 5a in a space S2 formed between the second filter member 6 b and thecylindrical portion 9, the mixed gas is discharged from the gasdischarge holes 8 formed in the cylindrical portion 9, to expand andinflate the airbag rapidly. Although the pressure in the interior of thehousing 3 increases at that time, since the housing 3 has a generallyspherical form, the housing 3 has a sufficient strength to withstand thepressure increase in the housing 3, suppressing deformation of thehousing to a very small range. Then, the high temperature gas generatedin the respective combustion chambers 5 a, 5 b passes through the filtermembers 6 a, 6 b placed in the respective combustion chambers 5 a, 5 b,bursts the rupture member 11, and is discharged from the gas dischargeholes 8. It is to be noted here that the ignition order of the firstigniter device 7 a and the second igniter device 7 b may be changed sothat the second igniter device 7 b can be put in operation, followed bythe operation of the first igniter device 7 a. Further, a selectivecontrol of the operation order of the igniter devices may be made, suchas, for example, igniting the both igniter devices 7 a, 7 bsimultaneously, in accordance with the collision shock pattern.

The gas generator according to the present invention may be varied asshown in FIG. 6. The gas generator A3 shown in FIG. 6 is a variant ofthe gas generator A2 of FIG. 5 wherein the partition plate 30 forpartitioning the combustion chamber 5 in the interior of the housing 3into the two chambers is changed in shape so that it has a sphericalshape or an oval spherical shape protruding toward the second combustionchamber 5 b on the upper side. This can provide the result that evenwhen an increased amount of gas generant 4 is packed in the firstcombustion chamber 5 a, deformation of the partition plate 30 issuppressed, and as such can prevent the gas from being bypassed from thefirst combustion chamber 5 a to the second combustion chamber 5 b by thedeformation of the partition plate 30.

As seen from the above, even when a plurality of igniter devices areused, since the housing has a generally spherical form or a generallyoval spherical form, the housing can be given an increased strength tosufficiently withstand the pressure increase even when reduced in sizeand weight.

Also, the airbag module of the present invention is so designed that thegas generator can be fixed to the airbag module through the flangedportion 12. The airbag module of the present invention is placed usuallyin the passenger's seat instrument panel, and a single gas generator isbuilt in the airbag module of the present invention.

EXAMPLES

In the following, the gas generator according to the present inventionis described with reference to Examples.

In the gas generator shown in FIGS. 1 and 2, a stainless material havinga thickness of 2 mm was pressed to form the closure shell having thefollowing dimensions: 75 mm in distance H between the bottoms of thehead portions 10, 14; 70 mm in diameter D₁ of the cylindrical portion 9;16 mm in h; 70 mm in major axis d₂ of the head portion 10 of the closureshell 2; 45 mm in minor axis d₁ of the same; and 45 mm in curvatureradius R of the head portion on the closure shell side. Also, astainless material having a thickness of 2 mm was pressed to form theinitiator shell 1 having the following dimensions: 67 mm in major axisd₂ of the head portion 14; 42 mm in minor axis d₁ of the same; and 20 mmin curvature radius r of the head portion on the initiator shell side.Then, the igniter device 7 and the filter member 6 were placed insequence in the initiator shell 1. Then, the gas generants 4 was packedin the inside of the filter member 6 and thereafter the cushioningmembers 22 are placed. Thereafter, the initiator shell 1 was fitted withthe closure shell 2. Then, the initiator shell 1 and the closure shell 2were joined together by laser welding to thereby produce the gasgenerator.

Reference Example

Example of manufacturing of gas generant of a form of a hollow bodyclosed at both ends used with the gas generator:

3 weight % ethanol and 13 weight % water were added to compositioncomprising a mixture of 43.5 weight % guanidine nitrate, 25 weight %strontium nitrate, 25 weight % basic copper nitrate, 2.5 weight % acidclay, and 4 weight % polyacrylamide and mixed and kneaded to therebyproduce a kneaded clod. The kneaded clod was extruded at an extrusionpressure of 8 MPa via an extruder having a die of an inner diameter of 2mm and an inner-hole pin of an outer diameter of 0.5 mm at an outletport thereof. Then, the molded product as extruded in a rod-like formwas fed into between molding teeth, while being taken off by a take-offbelt, to form depressed portions in the molded product at regularinterval of 4.4 mm by convex teeth. Then, the molded product was foldedat the depressed portions to cut it off. Thereafter, they were dried at55° C. for 8 hours and then were dried at 110° C. for 8 hours. The gasgenerants were formed in this manner.

CAPABILITY OF EXPLOITATION IN INDUSTRY

The gas generator according to the present invention is constructed asdescribed above. Since the housing is formed in a generally sphericalshape or a generally oval spherical shape, the housing can wellwithstand an increased inner pressure of the housing resulting from thegas generated by the burning of the gas generants, even when the gasgenerator is reduced in number of components and simplified instructure. This can suppress deformation of the housing at the time ofgeneration of gas to a very small range. This can provide a reducednumber of components and a simplified structure, thus enabling reductionin size and weight of the gas generator. This can also provide theeffect of providing a significant reduction of manufacturing cost, whilekeeping the safety of the gas generator.

1. A gas generator, comprising: a housing made of metal and including aninitiator shell and a closure shell; at least one combustion chamberformed in the housing and configured to be packed with a gas generantthat generates a high temperature gas by burning; at least one filtermember arranged around the at least one combustion chamber; at least oneigniter located in the housing and configured to ignite and burn the gasgenerant in the at least one combustion chamber; and a plurality of gasdischarge holes formed in the housing and configured to discharge gasgenerated in the at least one combustion chamber, wherein at least oneof the initiator shell and the closure shell forming the housingincludes a head portion of a semispherical form or an oval semisphericalform and a cylindrical portion having a diameter D formed continuouslyfrom the head portion, a ratio H/D between the diameter D of thecylindrical portion and a distance H between bottoms of the headportions of the initiator shell and closure shell is in a range of0.6-1.3, and the at least one filter member is configured so that aportion thereof around the gas discharge holes bulges inward to make theportion thick to prevent the at least one filter member from beingdamaged, and the filter member is configured so that, at each positionalong an axial direction of the gas generator, a thickness of the filtermember is substantially the same along a circumference of the filtermember.
 2. The gas generator according to claim 1, wherein a ratio d₁/d₂between a minor axis d₁ and a major axis d₂ of the head portion of theinitiator shell or the closure shell is in a range of 1-0.02.
 3. The gasgenerator according to claim 1, wherein the head portion has a crosssection of a generally semicircular shape or a generally semi-ellipticalshape formed with at least three continuously extending straight lines.4. The gas generator according to claim 1, wherein the head portion hasa semi-spherical form having a curvature radius R, and a ratio D/Rbetween the diameter D of the cylindrical portion and the curvatureradius R is in a range of 0.3-2.
 5. The gas generator according to anyone of claims 1 to 4, wherein the diameter D is a diameter D₁ betweenoutside surfaces of the closure shell.
 6. The gas generator according toclaim 1, wherein the cylindrical portion formed in the closure shell hasa height h in a range of 5-30 mm.
 7. The gas generator according toclaim 1, wherein the gas discharge holes are arranged in a zigzagpattern on a surface of the housing.
 8. The gas generator according toclaim 1, wherein the at least one igniter device includes an innercylinder having a base and a plurality of enhancer holes therearound, anenhancer agent packed in the inner cylinder, and an igniter placed incontact with the enhancer agent.
 9. The gas generator according to claim1, wherein the igniter device includes an inner cylinder having a baseand a plurality of enhancer holes therearound, an enhancer agent packedin the inner cylinder, and an igniter placed in contact with theenhancer agent, and the enhancer holes are arranged in a zigzag patternon a surface of the inner cylinder.
 10. The gas generator according toclaim 1, wherein the igniter device includes an inner cylinder having abase and a plurality of enhancer holes therearound, an enhancer agentpacked in the inner cylinder, and an igniter placed in contact with theenhancer agent, and each of the enhancer holes is formed on a surface ofa cylindrical portion of the inner cylinder in a form of a slot longalong an axial direction thereof.
 11. The gas generator according toclaim 1, wherein the igniter device includes an inner cylinder having abase and a plurality of enhancer holes therearound, an enhancer agentpacked in the inner cylinder, and an igniter placed in contact with theenhancer agent, and the enhancer holes are arranged in a zigzag patternon a surface of a cylindrical portion of the inner cylinder in a form ofslots along an axial direction thereof respectively.
 12. The gasgenerator according to of claim 1, wherein the gas generant is in theform of a hollow body closed at both ends.
 13. The gas generatoraccording to of claim 1, which is designed for a passenger's seat.
 14. Apassenger's seat airbag module to which the gas generator according toof claim 1 is fixed through a flanged portion.
 15. The gas generatoraccording to claim 1, wherein a thickest portion of the filter member isopposed to an entirety of the plurality of gas discharge holes such thata portion of the filter member that is directly below and in contactwith the thickest portion of the filter member, but is not opposed tothe plurality of gas discharge holes, is less thick than the thickestportion.
 16. A gas generator, comprising: a housing made of metal andincluding an initiator shell and a closure shell; a combustion chamberformed in the housing and configured to be packed with a gas generantthat generates a high temperature gas by burning; a partition plateconfigured to partition the combustion chamber into two tiered chambers;a first filter member and a second filter member arranged around thefirst partitioned combustion chamber and the second partitionedcombustion chamber respectively; a first igniter device and a secondigniter device located in the initiator shell and configured to igniteand burn the gas generant packed in the first partitioned combustionchamber and the second partitioned combustion chamber respectively; anda plurality of gas discharge holes formed in the housing and configuredto discharge gas generated in the first partitioned combustion chamberand the second partitioned combustion chamber, wherein at least one ofthe initiator shell and the closure shell forming the housing includes ahead portion of a semispherical form or an oval semispherical form and acylindrical portion of a diameter D formed continuously from the headportion, a ratio H/D between the diameter D of the cylindrical portionand a distance H between bottoms of the head portions of the initiatorshell and closure shell is in a range of 0.6-1.3, and at least one ofthe filter members is configured so that a portion thereof around thegas discharge holes bulges inward to make the portion thick to preventthe at least one filter member from being damaged, and the filter memberis configured so that, at each position along an axial direction of thegas generator, a thickness of the filter member is substantially thesame along a circumference of the filter member.
 17. The gas generatoraccording to claim 16, wherein a ratio d₁/d₂ between a minor axis d₁ anda major axis d₂ of the head portion of the initiator shell or closureshell is in a range of 1-0.02.
 18. The gas generator according to claim16, wherein the head portion has a cross section of a generallysemicircular shape or a generally semi-elliptical shape formed with atleast three continuously extending straight lines.
 19. The gas generatoraccording to claim 16, wherein the head portion has a semi-sphericalform having a curvature radius R, and a ratio D/R between the diameter Dof the cylindrical portion and the curvature radius R is in a range of0.3-2.
 20. The gas generator according to any one of claims 16 to 19,wherein the diameter D is a diameter D₁ between outer sides of theclosure shell.
 21. The gas generator according to claim 16, wherein thecylindrical portion has a height h in a range of 5-30 mm.
 22. The gasgenerator according to claim 16, wherein the gas discharge holes arearranged in a zigzag pattern on a surface of the housing.
 23. The gasgenerator according to claim 16, wherein the first igniter device andthe second igniter device include first and second inner cylinders eachhaving a base and a plurality of enhancer holes therearound, an enhanceragent packed in the first inner cylinder and the second inner cylinder,and a first igniter and a second igniter both being placed in contactwith the enhancer agent, respectively.
 24. The gas generator accordingto claim 16, wherein the first igniter device and the second igniterdevice include first and second inner cylinders each having a base and aplurality of enhancer holes therearound, an enhancer agent packed in thefirst inner cylinder and the second inner cylinder, and a first igniterand a second igniter both being placed in contact with the enhanceragent, respectively, and the enhancer holes are arranged in a zigzagpattern on surfaces of the first inner cylinder and the second innercylinder respectively.
 25. The gas generator according to claim 16,wherein the first igniter device and the second igniter device includefirst and second inner cylinders each having a base and a plurality ofenhancer holes therearound, an enhancer agent packed in the first innercylinder and the second inner cylinder, and a first igniter and a secondigniter both being placed in contact with the enhancer agent,respectively,-and the enhancer holes are formed on surfaces ofcylindrical portions of the first inner cylinder and the second innercylinder in a form of a slot long along axial directions thereof. 26.The gas generator according to claim 16, wherein the first igniterdevice and the second igniter device include first and second innercylinders each having a base and a plurality of enhancer holestherearound, an enhancer agent packed in the first inner cylinder andthe second inner cylinder, and a first igniter and a second igniter bothbeing placed in contact with the enhancer agent, respectively, theenhancer holes are arranged in a zigzag pattern on surfaces of the firstinner cylinder and the second inner cylinder, and the first innercylinder or the second inner cylinder is configured to be located in thesecond combustion chamber which is an upper side chamber of the twopartitioned chambers.
 27. The gas generator according to claim 16,wherein the first igniter device and the second igniter device includefirst and second inner cylinders each having a base and a plurality ofenhancer holes therearound, an enhancer agent packed in the first innercylinder and the second inner cylinder, and a first igniter and a secondigniter both being placed in contact with the enhancer agent,respectively,-and the enhancer holes, which are formed in either thefirst inner cylinder or the second inner cylinder in the form of acylinder having an extended axis, are configured to open only in thesecond combustion chamber which is located on an upper side of the twopartitioned chambers.
 28. The gas generator according to claim 16,wherein the partition plate is held between the initiator shell and theclosure shell.
 29. The gas generator according to claim 16, wherein athickest portion of the filter member is opposed to an entirety of theplurality of gas discharge holes such that a portion of the filtermember that is directly below and in contact with the thickest portionof the filter member, but is not opposed to the palarity of gasdischarge holes, is less thick than the thickest portion.
 30. A gasgenerator, comprising: a housing made of metal and including aninitiator shell and a closure shell; a combustion chamber formed in thehousing and configured to be packed with a gas generant that generates ahigh temperature gas by burning; a filter member arranged around thecombustion chamber; an igniter device located in the housing andconfigured to ignite and burn the gas generant in the combustionchamber; and a plurality of gas discharge holes formed in the housingand configured to discharge gas generated in the combustion chamber,wherein the housing has a generally spherical form, and the filtermember is configured so that a portion thereof around the gas dischargeholes bulges inward to make the portion thick to prevent the at leastone filter member from being damaged, and the filter member isconfigured so that, at each position along an axial direction of the gasgenerator, a thickness of the filter member is substantially the samealong a circumference of the filter member.
 31. The gas generatoraccording to claim 30, wherein a thickest portion of the filter memberis opposed to an entirety of the plurality of gas discharge holes suchthat a portion of the filter member that is directly below and incontact with the thickest portion of the filter member, but is notopposed to the plurality of gas discharge holes, is less thick than thethickest portion.
 32. A gas generator, comprising: a housing made ofmetal and including an initiator shell and a closure shell; a combustionchamber formed in the housing and configured to be packed with a gasgenerant that generates a high temperature gas by burning; a filtermember arranged around the combustion chamber; an igniter device locatedin the housing and configured to ignite and burn the gas generant in thecombustion chamber; and a plurality of gas discharge holes formed in thehousing and configured to discharge gas generated in the combustionchamber, wherein the housing has a generally oval form, and the at leastone filter member is configured so that a portion thereof around the gasdischarge holes bulges inward to make the portion thick to prevent theat least one filter member from being damaged, and the filter member isconfigured so that, at each position along an axial direction of the gasgenerator, a thickness of the filter member is substantially the samealong a circumference of the filter member.
 33. The gas generatoraccording to claim 32, wherein a thickest portion of the filter memberis opposed to an entirety of the plurality of gas discharge holes suchthat a portion of the filter member that is directly below and incontact with the thickest portion of the filter member, but is notopposed to the plurality of gas discharge holes, is less thick than thethickest portion.